This invention relates to a method for restoring used railroad ties having pre-existing spike holes, and more particularly to a method for plugging the pre-existing spike holes in the used railroad ties thereby forming the restored railroad ties which can be reused in rail replacement operations.
All maintenance of the rails in railroad operations typically means removing the rail spikes from the railroad ties. In many instances, these railroad ties are structurally usable because they have not deteriorated to a point requiring replacement. However, reusing these ties requires plugging of any spike holes existing in the railroad tie structure.
Generally, these spike holes can be plugged. In this way, when spikes are re-driven into the holes, the spikes will be firmly anchored within the confines of the ties.
In conventional practice, the ties are plugged by manually driving hardwood dowels into the spike holes. Unfortunately, the use of hardwood dowels results in several problems. First, the dowels do not completely fill the hole. This causes moisture infiltration during use that ultimately accelerates tie rot and in turn the deterioration of the railroad tie structure. Also, as compared with the original unused virgin railroad ties, the hardwood dowels do not effectively anchor the spikes into the structural railroad tie member.
The use of wood substrates and polymeric materials have been described in the prior art patents hereinafter cited, all of which are incorporated by reference in their entirety. Polymeric materials, such as rigid polymers and polymeric foams, have also been employed to fill spike holes in used railroad ties. U.S. Pat. No. 4,295,259 ("U.S. '259") describes filling spike holes in railroad, ties with a foamed polyurethane material. The polyurethane foam material is injected into the holes in wooden ties so that the foaming process takes place in the holes.
An important aspect of the invention described in U.S. '259 is the recognition that the density of the polyurethane foam plays a role in determining the usefulness of material chosen for filling spike holes. The range of about 1 lb/ft.sup.3 to 30 lb/ft.sup.3 is preferred.
Another major distinction promulgated by the invention of U.S. '259 relates to holding ability of the subject foamed polyurethane material. A summary of the experimental holding force data obtained are contained in Table 1 of U.S. '259. The holding forces shown in Table 1 are averages of the total data obtained. In the table, the material are ranked in decreasing order of their holding ability. The first column is the average of the pull force required to remove the spike after initially being driven into the tie itself ("A"). The next column is the average pull force with the plugging material ("B"). The ratio ("Ratio") of the pulling force with the plugging material with the plugging material to the initial pulling force ("B/A") is listed in the third column. The highest Ratio shown in Table 1 is 0.77. According to U.S. '259, no polymeric filler material employed in the scope of their invention was able to create a filled tie spike hole and having a holding ability greater than 77% of the initial pulling strength of the railroad tie. The data also indicates that these effective filler materials have a density of 30 lbs/ft.sup.3 or less.
A major disadvantage of using polymeric foams, for example, is the instability caused to them by environmental moisture. During rainy conditions, or in high humidity, these foamed materials react with water or moisture causing them to foam excessively. This excess foaming substantially reduces the ability of the filled polymeric material to anchor the tie. Moreover, polymeric foams, such as for example polyurethane foams, can stove-pipe out of a spike hole due to the reaction of a polyurethane material with water. This creates several negative consequences. First, it causes the polyurethane filler material to exhibit reduced Spike Withdrawal Lateral Resistance. Secondly, it also creates copious quantities of excess foam debris (which look like large snow balls) to dispose of thereby needlessly wasting time and materials. The debris typically must be sheared off the tie plate prior to re-spiking. This makes it difficult for a user to drive a spike into the pre-existing hole because the excess foam interferes with an effective and efficient re-spiking operation. Stated another way, this also presents a significant increase in the time required to complete the re-spiking operation for users in the field.
Third, another disadvantage with regard to use of polymeric foam filling agents is tie rot. This problem results from moisture infiltration into the space formed between the foam material and the spike hole wood surface.
Due to the problems as discussed above, the use of polymeric foam materials to fill spike holes in railroad ties have had limited commercial success in the railroad industry over the past twenty years. Therefore, wood plugs continue to dominate the railroad tie maintenance industry.
Other prior patents, such as U.S. Pat. No. 4,522,127, disclose a railroad tie plug driving apparatus. The apparatus drives plugs into railway tie holes remaining after the removal of at least one rail and its associated tie plate and rail spikes from the railway ties. Other machines for driving railroad tie plugs are described in U.S. Pat. No. 3,114,331 and U.S. Pat. No. 3,144,835. Railroad tie plugs of various configurations are disclosed in U.S. Pat. No. 620,060 and U.S. Pat. No. 1,338,444. U.S. Pat. No. 4,785,692, is directed to a tool for driving wooden plugs into wooden spike holes of railroad ties following removal of railroad spikes from the wooden tie prior to track regauging and/or replacement.
U.S. Pat. No. 4,626,189, U.S. Pat. No. 4,738,808, and U.S. Pat. No. 4,824,627, each relate to a method of making a molded plastic product. A large wooden object such as a railroad tie can be molded within the plastic material.
U.S. Pat. No. 4,070,201 discloses the use of a spike hole plugging material. A method is also provided involving a substantially uniform mixture of about 25-75% granular abrasive material, and about 25-75% granular plastic material. The problems associated with this railroad tie spike hole plugging technique is clearly set forth in the hereinafter cited U.S. Pat. No. 4,295,259 patent.
U.S. Pat. No. 4,134,546 is directed to a cylindrical insert of cellular plastic which is introduced into a wooden rail support structure. The insertion process is accomplished by boring a hole into the wooden structure. Then, the cylindrical plastic foam insert is introduced into the hole. Finally, a tie plate and a rail are positioned thereon and can be fastened thereto for receiving and holding a fastening device such as a rail tie.
Therefore, a need exists for an effective and efficient method for filling spike holes in used railroad ties which will then produce restored filled railroad ties which can be reused in rail replacement operations. Such a method should preferably have the following attributes: (a) firmly anchoring the spike into the tie; (b) deeply infiltrate the small cracks and crevices in the wood surface forming the spike hole to impede tie rot due to moisture; (c) bond tightly with the wood to prevent moisture infiltration; (d) be re-spikable within a relatively short time after dispensing; (e) displace standing water in tie holes during the hole filling operation; (f) dams leaky tie holes to enable complete filling; capable of having the railroad spike penetrate the filled material without substantial bending problems. As for the filled portion of the railroad tie, it should anchor the spike in a manner which is comparable to introducing a railroad spike into the virgin wood portion of the subject railroad tie.